The present invention relates to a hydrogenation catalyst which comprises nickel on a TiO2 support. The catalyst is used particularly for the hydrogenation of nitroaromatic compounds to form the corresponding aromatic amino compounds.
The use of nickel-containing catalysts as hydrogenation catalysts has been known for a long time. In Russian Journal of Applied Chemistry, Vol. 70, No. 8, 1997, pages 1236 to 1253, the preparation of such nickel-containing catalysts is described in detail. The catalysts described comprise nickel predominantly on silicon dioxide or aluminum oxide as support.
They can be prepared by precipitation onto the support or by coprecipitation. Use is also made of SiO2/TiO2 supports, and it is indicated that TiO2 as modifier can lead to mechanically stable catalysts.
DD-A-152 065 relates to a process for the hydrogenation of nitroaromatics using stirring-stable suspension catalysts. The catalyst is prepared by precipitation of a nickel salt solution in the presence of silica gel having a particular particle size distribution.
DD-A-284 371 relates to a process for the reduction of nitroaromatics in the presence of an Ni/SiO2 catalyst. The catalyst is supported on a support having a size of more than 1 mm and is passivated after activation. Prior to the reaction, the catalyst is milled in the reactor.
U.S. Pat. No. 3,868,332 relates to a hydrogenation catalyst which is used, in particular, for the conversion of benzene into cyclohexane. The catalyst is prepared by coprecipitation of nickel and silicate ions in the presence of a porous silicon dioxide support.
WO 95/14647 relates to a process for the oligomerization of olefins to form highly linear oligomers. The process is carried out using an oxidic catalyst comprising nickel oxide, silicon dioxide and titanium dioxide and also an alkali metal oxide. The catalyst is prepared by coprecipitation of a nickel salt solution onto finely divided titanium dioxide powder by means of a sodium water glass solution. Nickel is present in oxidic form, and the catalyst is used in the form of pressed pellets as a fixed bed. Use as hydrogenation catalyst is not described.
DE-A-199 09 176 and DE-A-199 09 168 relate to hydrogenation catalysts comprising nickel and frequently zirconium on a zirconium-containing support.
In the hydrogenation of nitroaromatic compounds to form aromatic amino compounds, the catalyst is exposed to a strongly alkaline medium. A catalyst dispersed in the reaction medium is subjected to high mechanical stresses when the reaction mixture is circulated or stirred. It should have a particle size distribution such that it can be both readily dispersed and readily separated off under operating conditions.